Chlorosulfonated polyethylene elastomers are manufactured by dissolving polyethylene in a solvent such as carbon tetrachloride, along with a catalyst, and bubbling chlorine and sulfur dioxide through the solution to obtain a polymer containing about 20 to 40 percent chlorine and about 1 to 2 percent sulfur present in secondary sulfonyl chloride groups. The chlorosulfonated polyethylene is isolated from the solvent and dried. The use of a solvent requires large equipment for handling the dilute solutions; more equipment to isolate the polymer from the solvent, and still more equipment to recover and purify the solvent for reuse. In addition to processing and utilities costs, chlorinated solvents present toxicological problems. In large scale applications it is necessary to protect workers and to prevent contamination of the atmosphere with carbon tetrachloride or other solvents. Further, chlorosulfonation in solution is difficult with many high molecular weight, high density polyolefins.